Multilayer ceramic capacitor and manufacturing method of multilayer ceramic capacitor

ABSTRACT

A multilayer ceramic capacitor includes: a multilayer structure in which each of a plurality of dielectric layers and each of a plurality of internal electrode layers are alternately stacked, wherein a concentration of a rare earth element in an active region with respect to a main component ceramic of the active region is equal to or more than a concentration of a rare earth element in at least a part of a protective region with respect to a main component ceramic of the protective region, wherein an average ionic radius of the rare earth element of the at least a part of the protective region is equal to or less than an average ionic radius of the rare earth element in the active region.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2018-095454, filed on May 17,2018, the entire contents of which are incorporated herein by reference.

FIELD

A certain aspect of the present invention relates to a multilayerceramic capacitor and a manufacturing method of the multilayer ceramiccapacitor.

BACKGROUND

Multilayer ceramic capacitors include an active region and a protectiveregion. The active region has a structure in which one set of internalelectrodes connected to one external electrode and another set ofinternal electrodes connected to the other external electrode face witheach other and has an electrical capacity. The protective region hascover layers sandwiching the active region in an up-down direction and aside margin region sandwiching the active region in a lateral direction.Densifying of the protective region in a firing process may be slowerthan that of the active region and humidity resistance of the protectiveregion may be degraded, because a diffusion amount of a metal of theprotective region is smaller than that of the internal electrode and adensity of a compact before the firing is small. Therefore, in order topromote the densifying of the protective region, the active region isfired in a temperature higher than an optimal firing temperature of theactive region.

SUMMARY OF THE INVENTION

The present invention has a purpose of providing a multilayer ceramiccapacitor and a manufacturing method of the multilayer ceramic capacitorthat are capable of suppressing degradation of characteristic andimproving sintering characteristic of a protective region.

According to an aspect of the present invention, there is provided amultilayer ceramic capacitor including: a multilayer structure in whicheach of a plurality of dielectric layers and each of a plurality ofinternal electrode layers are alternately stacked, a main component ofthe dielectric layers being ceramic, the multilayer structure having arectangular parallelepiped shape, the plurality of internal electrodelayers being alternately exposed to a first end face and a second endface of the multilayer structure, the first end face facing with thesecond end face, wherein a concentration of a rare earth element in anactive region with respect to a main component ceramic of the activeregion is equal to or more than a concentration of a rare earth elementin at least a part of a protective region with respect to a maincomponent ceramic of the protective region, wherein the active region isa region in which a set of internal electrode layers exposed to thefirst end face of the multilayer structure face with another set ofinternal electrode layers exposed to the second end face of themultilayer structure, wherein the protective region includes a coverlayer and a side margin, wherein the cover layer is provided on at leastone of an upper face and a lower face of the multilayer structure in astacking direction of the multilayer structure, a main component of thecover layer being a same as that of the dielectric layers, wherein, inthe multilayer structure, the side margin covers edge portions to whichthe plurality of internal electrode layers extend toward two side facesother than the first end face and the second end face, wherein anaverage ionic radius of the rare earth element of the at least a part ofthe protective region is equal to or less than an average ionic radiusof the rare earth element in the active region.

According to another aspect of the present invention, there is provideda manufacturing method of a multilayer ceramic capacitor including: afirst process of forming a stack unit by providing a pattern of metalconductive paste on a green sheet having grains of main componentceramic; a second process of stacking a plurality of the stack unitsformed in the first process so that positions of the patterns arealternately shifted to each other; a third process of forming two endfaces and two side faces in a ceramic multilayer structure obtained inthe second process, by cutting the ceramic multilayer structure, the twoend faces being faces to which a plurality of the patterns arealternately exposed, the two side faces being faces to which all of thepatterns are exposed; and a fourth process of providing side marginsheets on the two side faces, the side margin sheet including grains ofmain component ceramic and firing the ceramic multilayer structuretogether with the side margin sheets, wherein a concentration of a rareearth element in the green sheet with respect to the main componentceramic of the green sheet is equal to or more than a concentration of arare earth element in the side margin sheet with respect to the maincomponent ceramic of the side margin sheet, wherein an average ionicradius of the rare earth element of the side margin sheet is equal to orless than an average ionic radius of the rare earth element of the greensheet.

According to another aspect of the present invention, there is provideda manufacturing method of a multilayer ceramic capacitor including: afirst process of forming a stack unit by providing a pattern of metalconductive paste on a green sheet having grains of main componentceramic; a second process of stacking a plurality of the stack unitsformed in the first process so that positions of the patterns arealternately shifted to each other; and a third process of providingcover sheets on an upper face and a lower face in a stacking directionof a ceramic multilayer structure obtained in the second process, thecover sheets including grains of main component ceramic, wherein aconcentration of a rare earth element in the green sheet with respect tothe main component ceramic of the green sheet is equal to or more than aconcentration of a rare earth element in the cover sheets with respectto the main component ceramic of the cover sheets, wherein an averageionic radius of the rare earth element of the cover sheets is equal toor less than an average ionic radius of the rare earth element of thegreen sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a partial perspective view of a multilayer ceramiccapacitor;

FIG. 2 illustrates a cross sectional view taken along a line A-A of FIG.1;

FIG. 3 illustrates a cross sectional view taken along a line B-B of FIG.1;

FIG. 4 illustrates a manufacturing method of a multilayer ceramiccapacitor; and

FIG. 5 illustrates measured a position of a crystal grain diameter.

DETAILED DESCRIPTION

When the firing temperature is high, a continuity modulus of theinternal electrode layer may be degraded. The continuity modulus of theinternal electrode has large influence on reliability of the multilayerceramic capacitor. Therefore, when the firing temperature is high,sufficient reliability may not be necessarily achieved.

In order to improve the sintering characteristic of the protectiveregion without increasing the firing temperature, Si (silicon) or aglass component acting as a sintering assistant is added to theprotective region (for example, see Japanese Patent ApplicationPublication No. 2011-124429). The glass component is such as silicateglass, borate glass, borosilicate glass, phosphate glass, or the likeincluding an alkali metal component such as Li (lithium), Na (sodium), K(potassium) or an alkali earth metal component such as Ca (calcium), Ba(barium), Sr (strontium). However, with the method, diffusion may occurbecause of a difference between the composition of the active region andthe composition of the protective region. Si or the glass componentacting as the sintering assistant may cause excessive grain growth orreduction of the dielectric constant, when Si or the glass componentdiffuses into the active region. Alternatively, there are methods foradding an element such as Mn (manganese) or Mg (magnesium) to promotedensifying (for example, see Japanese Patent Application Publication No.2017-011172). However, Mn or Mg may reduce an efficient capacity of theactive region. Therefore, when the additive element to promote sinteringof the protective region diffuses into the active region, thecharacteristic of the multilayer ceramic capacitor may be degraded.

A description will be given of an embodiment with reference to theaccompanying drawings.

Embodiment

FIG. 1 illustrates a partial perspective view of a multilayer ceramiccapacitor 100 in accordance with an embodiment. FIG. 2 illustrates across sectional view taken along a line A-A of FIG. 1. FIG. 3illustrates a cross sectional view taken along a line B-B of FIG. 1. Asillustrated in FIG. 1 to FIG. 3, the multilayer ceramic capacitor 100includes a multilayer chip 10 having a rectangular parallelepiped shape,and a pair of external electrodes 20 a and 20 b that are respectivelyprovided at two end faces of the multilayer chip 10 facing each other.In four faces other than the two end faces of the multilayer chip 10,two faces other than an upper face and a lower face of the multilayerchip 10 in a stacking direction are referred to as side faces. Theexternal electrodes 20 a and 20 b extend to the upper face, the lowerface and the two side faces of the multilayer chip 10. However, theexternal electrodes 20 a and 20 b are spaced from each other.

The multilayer chip 10 has a structure designed to have dielectriclayers 11 and internal electrode layers 12 alternately stacked. Thedielectric layer 11 includes ceramic material acting as a dielectricmaterial. The internal electrode layers 12 include a base metalmaterial. End edges of the internal electrode layers 12 are alternatelyexposed to a first end face of the multilayer chip 10 and a second endface of the multilayer chip 10 that is different from the first endface. In the embodiment, the first end face faces with the second endface. The external electrode 20 a is provided on the first end face. Theexternal electrode 20 b is provided on the second end face. Thus, theinternal electrode layers 12 are alternately conducted to the externalelectrode 20 a and the external electrode 20 b. Thus, the multilayerceramic capacitor 100 has a structure in which a plurality of dielectriclayers 11 are stacked and each two of the dielectric layers 11 sandwichthe internal electrode layer 12. In the multilayer chip 10, the internalelectrode layer 12 is positioned at an outermost layer. The upper faceand the lower face of the multilayer chip 10 that are the internalelectrode layers 12 are covered by cover layers 13. A main component ofthe cover layer 13 is a ceramic material. For example, a main componentof the cover layer 13 is the same as that of the dielectric layer 11.

For example, the multilayer ceramic capacitor 100 may have a length of0.25 mm, a width of 0.125 mm and a height of 0.125 mm. The multilayerceramic capacitor 100 may have a length of 0.4 mm, a width of 0.2 mm anda height of 0.2 mm. The multilayer ceramic capacitor 100 may have alength of 0.6 mm, a width of 0.3 mm and a height of 0.3 mm. Themultilayer ceramic capacitor 100 may have a length of 1.0 mm, a width of0.5 mm and a height of 0.5 mm. The multilayer ceramic capacitor 100 mayhave a length of 3.2 mm, a width of 1.6 mm and a height of 1.6 mm. Themultilayer ceramic capacitor 100 may have a length of 4.5 mm, a width of3.2 mm and a height of 2.5 mm. However, the size of the multilayerceramic capacitor 100 is not limited.

A main component of the internal electrode layers 12 is a base metalsuch as nickel (Ni), copper (Cu), tin (Sn) or the like. The internalelectrode layers 12 may be made of a noble metal such as platinum (Pt),palladium (Pd), silver (Ag), gold (Au) or alloy thereof. An averagethickness of the internal electrode layer 12 is, for example, 1 μm orless. The dielectric layers 11 are mainly composed of a ceramic materialthat is expressed by a general formula ABO₃ and has a perovskitestructure. The perovskite structure includes ABO_(3-α) having anoff-stoichiometric composition. For example, the ceramic material issuch as BaTiO₃ (barium titanate), CaZrO₃ (calcium zirconate), CaTiO₃(calcium titanate), SrTiO₃ (strontium titanate),Ba_(1-x-y)Ca_(x)Sr_(y)Ti_(1-z)Zr_(z)O₃ (0≤x≤1, 0≤y≤1, 0≤z≤1) having aperovskite structure. An average thickness of the dielectric layer 11is, for example, 1 μm or less.

As illustrated in FIG. 2, a region, in which a set of the internalelectrode layers 12 connected to the external electrode 20 a faceanother set of the internal electrode layers 12 connected to theexternal electrode 20 b, is a region generating electrical capacity inthe multilayer ceramic capacitor 100. And so, the region is referred toas an active region 14. That is, the active region 14 is a region inwhich the internal electrode layers 12 next to each other are connectedto different external electrodes face each other.

A region, in which the internal electrode layers 12 connected to theexternal electrode 20 a face with each other without sandwiching theinternal electrode layer 12 connected to the external electrode 20 b, isreferred to as an end margin region 15. A region, in which the internalelectrode layers 12 connected to the external electrode 20 b face witheach other without sandwiching the internal electrode layer 12 connectedto the external electrode 20 a is another end margin region 15. That is,the end margin region 15 is a region in which a set of the internalelectrode layers 12 connected to one external electrode face with eachother without sandwiching the internal electrode layer 12 connected tothe other external electrode. The end margin region 15 is a region thatdoes not generate electrical capacity in the multilayer ceramiccapacitor 100.

As illustrated in FIG. 3, a region of the multilayer chip 10 from thetwo sides thereof to the internal electrode layers 12 is referred to asa side margin region 16. That is, the side margin region 16 is a regioncovering edges of the stacked internal electrode layers 12 in theextension direction toward the two side faces. The side margin region 16does not generate electrical capacity. In the following description, thecover layers 13 and the side margin region 16 that surround the activeregion 14 without generating the electrical capacity may be called as aprotective region.

It is possible to form the active region 14 and the protective region bysintering a powder material. Densifying of the protective region in afiring process may be slower than that of the active region 14 andhumidity resistance of the protective region may be degraded, because adiffusion amount of a metal structuring the internal electrode layer 12in the protective region is smaller than that in the active region 14and a density of a compact before the firing is small. Therefore, inorder to promote the densifying of the protective region, the activeregion 14 is fired in a temperature higher than an optimal firingtemperature of the active region 14. However, when the firingtemperature is high, a continuity modulus of the internal electrodelayer 12 may be degraded. The continuity modulus of the internalelectrode layer 12 has large influence on the reliability of themultilayer ceramic capacitor 100. Therefore, when the firing temperatureis high, sufficient reliability may not be necessarily achieved.

In order to improve the sintering characteristic of the protectiveregion without increasing the firing temperature, Si or a glasscomponent acting as a sintering assistant may be added to the protectiveregion. However, with the method, diffusion may occur because of adifference between the composition of the active region 14 and thecomposition of the protective region. Si or the glass component actingas the sintering assistant may cause excessive grain growth or reductionof the dielectric constant, when Si or the glass component diffuses intothe active region 14. Alternatively, there are methods for adding anelement such as Mn or Mg to promote densifying. However, Mn or Mg mayreduce an efficient capacity of the active region 14. Therefore, whenthe additive element to promote sintering of the protective regiondiffuses into the active region 14, the characteristic of the multilayerceramic capacitor 100 may be degraded.

And so, it is thought that the densifying of the active region 14 isdelayed. When the densifying of the active region 14 is delayed, it ispossible to reduce the difference of the densifying between the activeregion 14 and the protective region. It is therefore possible to improvethe sintering characteristic of the protective region without increasingthe firing temperature. The embodiment focuses on a rare earth element.The rare earth element is added in order to secure the reliability ofthe multilayer ceramic capacitor 100. The rare earth element improvesthe reliability of the multilayer ceramic capacitor 100. On the otherhand, the rare earth element increases the temperature for terminatingthe densifying and delays the densifying. And so, in the embodiment, aconcentration of an added rare earth element is determined. In concrete,the concentration of the rare earth element in the active region 14 isequal to or more than the concentration of the rare earth element in theprotective region. Thus, it is possible to reduce the difference of thedensifying of the active region 14 and the densifying of the protectiveregion. In this case, even if the firing temperature is not excessivelyincreased, it is possible to densify both the active region 14 and theprotective region. It is therefore possible to improve the humidityresistance while the reduction of the continuity modulus of the internalelectrode layer 12 is suppressed. It is not necessary to add the elementto promote the densifying of the protective region. Therefore, thediffusion of the additive element added to the active region 14 issuppressed. It is therefore possible to suppress characteristicdegradation of the multilayer ceramic capacitor 100. The concentrationof the rare earth element is a concentration with respect to the maincomponent ceramic. Therefore, the concentration of the rare earthelement is atm % on a presumption that the concentration of the B siteelement of ABO₃ of the main component ceramic is 100 atm %.

However, when the grain growth is promoted in the protective region, thegrain growth is promoted in a part of the active region 14 near theprotective region. In this case, the reliability may be degraded. Andso, the embodiment focuses on an average ionic radius of the rare earthelement. When the ionic radius of the rare earth element is small, aratio of the rare earth element that is solid-solved in the B sitehaving a relatively small ionic radius increases. When the ionic radiusof the rare earth element is large, a ratio of the rare earth elementthat is solid-solved in the A site having a relatively large ionicradius increases. In ABO₃ of the perovskite structure, a diffusion speedin the A site is higher than a diffusion speed in the B site because ofa crystal structure of the perovskite structure. Therefore, when therare earth element having a small ionic radius is added, the gain growthtends to be suppressed. And so, in the embodiment, the average ionicradius of the rare earth element is determined. In concrete, the averageionic radius of the rare earth element in the protective region is equalto or less than the average ionic radius of the rare earth element inthe active region 14. In this case, the grain growth of the protectiveregion is suppressed. Thereby, the grain growth of the part of theactive region 14 near the protective region is suppressed. It istherefore possible to improve the reliability of the active region 14.When one type of the rare earth element is added, the average ionicradius means an ionic radius of the rare earth element. When two or moretypes of the rare earth elements are added, the average ionic radiusmeans an arithmetic average of the concentrations of the rare earthelements on the basis of the concentrations ratio.

Y (yttrium), La (lanthanum), Ce (cerium), Pr (praseodymium), Nd(neodymium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb(terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb(ytterbium) or the like can be used as the rare earth element. Table 1shows ionic radiuses of rare earth elements of which a valence is 3 andof which a coordination number is 6. Exhibition of Table 1 is “R. D.Shannon, Acta Crystallogr., A32, 751(1976)”.

TABLE 1 IONIC RADIUS (Å) COORDINATION COORDINATION VALENCE NUMBER IS 6NUMBER IS 12 Ba +2 1.610 Ti +4 0.605 La +3 1.032 Ce +3 1.010 Pr +3 0.990Nd +3 0.983 Sm +3 0.958 Eu +3 0.947 Gd +3 0.938 Tb +3 0.923 Dy +3 0.912Ho +3 0.901 Y +3 0.900 Er +3 0.890 Tm +3 0.880 Yb +3 0.868

When the concentration of the rare earth element is excessively small,sufficient reliability may not be necessarily achieved. And so, it ispreferable that the concentration of the rare earth element has a lowerlimit. For example, it is preferable that the concentration of the rareearth element in the active region 14 is 0.5 atm % or more. It is morepreferable that the concentration of the rare earth element in theactive region 14 is 0.7 atm % or more. It is preferable that theconcentration of the rare earth element in the protective region is 0.5atm % or more. It is more preferable that the rare earth element in theprotective region is 0.7 atm % or more. On the other hand, when theconcentration of the rare earth element is excessively high, thesintering characteristic itself may be degraded and it may be necessaryto form the internal electrode layer 12 by a firing of a hightemperature which is not preferable for high continuity modulus of theinternal electrode layer 12. And so, it is preferable that theconcentration of the rare earth element has an upper limit. It ispreferable that the concentration of the rare earth element in theactive region 14 is 2.0 atm % or less. It is more preferable that theconcentration of the rare earth element in the active region 14 is 1.8atm % or less. It is preferable that the concentration of the rare earthelement in the protective region is 2.0 atm % or less. It is morepreferable that the concentration of the rare earth element is 1.8 atm %or less.

When a difference between the concentration of the rare earth element inthe active region 14 and the concentration of the rare earth element inthe protective region is excessively large, the diffusion of the rareearth element from the active region 14 to the protective region isremarkable and the reliability of the active region 14 near theprotective region may be degraded. And so, it is preferable that thedifference has an upper limit. In concrete, it is preferable that thedifference between the concentration (atm %) of the rare earth elementin the active region 14 and the concentration (atm %) of the rare earthelement in the protective region is 0 or more and 0.5 or less.

The rare earth element included in the active region 14 and theprotective region is not limited. However, it is preferable that therare earth element can be substitutionally solid-solved in both the Asite and the B site. For example, ionic radiuses of La, Ce, Pr, Nd, Smand Eu are large, when the main component ceramic is BaTiO₃. Therefore,La, Ce, Pr, Nd, Sm and Eu tend to be substitutionally solid-solved inthe A site. Therefore, even if these rare earth element having a largeionic radius are added together with an element such as Er or Yb havingrelatively small ionic radius, it is difficult to achieve preferablebalance between the solid-solution in the A site and the solid-solutionin the B site. And, it is difficult to achieve high reliability. And so,it is preferable that the rare earth element included in the activeregion 14 and the protective region is at least one of Gd, Tb, Dy, Ho,Er, Y and Yb. For example, when one type of rare earth elements is used,it is preferable that the rare earth element is Dy, Ho, Er or Y. When anelement having a large ionic radius is added together with an elementhaving a small ionic radius, it is preferable that, among Gd, Tb, Dy,Ho, Er, Y and Yb, an element having a large ionic radius and an elementhaving a small ionic radius are added together with each other (forexample, Gd and Yb).

In the above-mentioned example, (the concentration of the rare earthelement in the active region 14) is equal to or more than (theconcentration of the rare earth element in the protective region). And(an average ionic radius of the rare earth element in the active region14) is equal to or more than (an average ionic radius of the rare earthelement in the protective region). However, the relationship is notlimited. At least a part of the protective region satisfies theabove-mentioned formulas. Alternatively, a whole of at least one of thecover layer 13 and the side margin region 16 satisfies theabove-mentioned formulas.

Next, a description will be given of a manufacturing method of themultilayer ceramic capacitor 100. FIG. 4 illustrates a manufacturingmethod of the multilayer ceramic capacitor 100.

(Making Process of Raw Material Powder)

A dielectric material for forming the dielectric layer 11 is prepared.Generally, an A site element and a B site element are included in thedielectric layer 11 in a sintered phase of grains of ABO₃. For example,BaTiO₃ is tetragonal compound having a perovskite structure and has ahigh dielectric constant. Generally, BaTiO₃ is obtained by reacting atitanium material such as titanium dioxide with a barium material suchas barium carbonate and synthesizing barium titanate. Various methodscan be used as a synthesizing method of the ceramic structuring thedielectric layer 11. For example, a solid-phase method, a sol-gelmethod, a hydrothermal method or the like can be used.

Additive compound may be added to the resulting ceramic powder inaccordance with purposes. The additive compound may be an oxide of Mo(molybdenum), Nb (niobium), Ta (tantalum), W (tungsten), Mn, V(vanadium), Cr (chromium) or a rare earth element, or an oxide of Co(cobalt), Ni, Li, B, Na, K and Si, or glass.

In the embodiment, it is preferable that ceramic particles structuringthe dielectric layer 11 are mixed with compound including additives andare calcined in a temperature range from 820 degrees C. to 1150 degreesC. Next, the resulting ceramic particles are wet-blended with additivesand are dried and crushed. Thus, a ceramic powder is obtained. Forexample, it is preferable that an average grain diameter of theresulting ceramic powders is 50 nm to 300 nm. For example, the graindiameter may be adjusted by crushing the resulting ceramic powder asneeded. Alternatively, the grain diameter of the resulting ceramic powermay be adjusted by combining the crushing and classifying.

Next, a cover material for forming the cover layer 13 is prepared. Anadditive compound may be added to ceramic powders of barium titanateobtained by the same process as the dielectric material, in accordancewith purposes. The additive compound may be an oxide of Mn, V, Cr or arare earth element, or an oxide of Co, Ni, Li, B, Na, K and Si, orglass. In the embodiment, the concentration of the rare earth element ofthe cover material with respect to the main component ceramic of thecover material is equal to or less than the concentration of the rareearth element of the dielectric material with respect to the maincomponent ceramic of the dielectric material. And, the average ionicradius of the rare earth element of the cover material is equal to orless than the ionic radius of the rare earth element of the dielectricmaterial.

In the embodiment, it is preferable that ceramic particles structuringthe cover material are mixed with compound including additives and arecalcined in a temperature range from 820 degrees C. to 1150 degrees C.Next, the resulting ceramic particles are wet-blended with additives,are dried and crushed. Thus, ceramic powder is obtained. For example, itis preferable that an average grain diameter of the resulting ceramicpowders is 50 nm to 300 nm as well as the dielectric material. The graindiameter may be adjusted by crushing the resulting ceramic powder asneeded. Alternatively, the grain diameter of the resulting ceramic powermay be adjusted by combining the crushing and classifying.

Next, a side margin material for forming the side margin region 16 isprepared. Additive compound may be added to ceramic powder of bariumtitanate obtained by the same process as the dielectric material, inaccordance with purposes. The additive compound may be an oxide of Mn,V, Cr or a rare earth element, or an oxide of Co, Ni, Li, B, Na, K andSi, or glass. In the embodiment, the concentration of the rare earthelement with respect to the main component ceramic of the side marginmaterial is equal to or less than the concentration of the rare earthelement with respect to the main component ceramic of the dielectricmaterial. And the average ionic radius of the rare earth element of theside margin material is equal to or less than the average ionic radiusof the rare earth element in the dielectric material. The cover materialmay be the same as the side margin material.

In the embodiment, it is preferable that ceramic particles structuringthe side margin material are mixed with compound including additives andare calcined in a temperature range from 820 degrees C. to 1150 degreesC. Next, the resulting ceramic particles are wet-blended with additives,are dried and crushed. Thus, ceramic powder is obtained. For example, itis preferable that an average grain diameter of the resulting ceramicpowders is 50 nm to 300 nm, as well as the dielectric material. Thegrain diameter may be adjusted by crushing the resulting ceramic powderas needed. Alternatively, the grain diameter of the resulting ceramicpower may be adjusted by combining the crushing and classifying.

(Stacking Process)

Next, a binder such as polyvinyl butyral (PVB) resin, an organic solventsuch as ethanol or toluene, and a plasticizer are added to the resultingdielectric material and wet-blended. With use of the resulting slurry, astripe-shaped dielectric green sheet with a thickness of 1.0 μm or lessis coated on a base material by, for example, a die coater method or adoctor blade method, and then dried.

Then, a pattern of the internal electrode layer 12 is provided on thesurface of the dielectric green sheet by printing metal conductive pastefor forming an internal electrode with use of screen printing or gravureprinting. The conductive paste includes an organic binder. A pluralityof patterns are alternatively exposed to the pair of externalelectrodes. The metal conductive paste includes ceramic particles as aco-material. A main component of the ceramic particles is not limited.However, it is preferable that the main component of the ceramicparticles is the same as that of the dielectric layer 11. For example,BaTiO₃ having an average grain diameter of 50 nm or less may be evenlydispersed.

Then, the dielectric green sheet on which the internal electrode layerpattern is printed is stamped into a predetermined size, and apredetermined number (for example, 100 to 500) of stamped dielectricgreen sheets are stacked while the base material is peeled so that theinternal electrode layers 12 and the dielectric layers 11 are alternatedwith each other and the end edges of the internal electrode layers 12are alternately exposed to both end faces in the length direction of thedielectric layer 11 so as to be alternately led out to a pair ofexternal electrodes 20 a and 20 b of different polarizations.

Next, a binder such as polyvinyl butyral (PVB) resin, an organic solventsuch as ethanol or toluene, and a plasticizer are added to the covermaterial and wet-blended. With use of the resulting slurry, astripe-shaped dielectric cover sheet with a thickness of 10 μm or lessis coated on a base material by, for example, a die coater method or adoctor blade method, and then dried. The cover sheets, which are to bethe cover layers 13, are compressed on the stacked dielectric greensheets and under the stacked dielectric green sheets. The resultingmultilayer structure is cut into a predetermined size. In this case, thestacked structure has two end faces to which a plurality of internalelectrode layer patterns are alternately exposed and two side faces towhich all of the internal electrode layer patterns are exposed.

Next, a binder such as polyvinyl butyral (PVB) resin, an organic solventsuch as ethanol or toluene, and a plasticizer are added to the sidemargin material and wet-blended. With use of the resulting slurry, astripe-shaped side margin sheet with a thickness of 30 μm or less iscoated on a base material by, for example, a die coater method or adoctor blade method, and then dried. The side margin sheets, which areto be the side margin region 16, are compressed on the two side faces ofthe stacked structure of the dielectric green sheets. The binder isremoved from the resulting stacked structure in N₂ atmosphere of atemperature range of 250 degrees C. to 500 degrees C. After that, metalconductive paste to be the external electrodes 20 a and 20 b are coatedon the both end of the stacked structure by a dipping method or the likeand is dried. Thus, a compact of the multilayer ceramic capacitor 100 isobtained.

(Firing Process)

The resulting compact is fired for ten minutes to 2 hours in a reductiveatmosphere having an oxygen partial pressure of 10⁻⁵ to 10⁻⁸ atm in atemperature range of 1100 degrees C. to 1300 degrees C. Thus, eachcompound is sintered and grown into grains. In this manner, it ispossible to manufacture the multilayer ceramic capacitor 100.

(Re-Oxidizing Process)

After that, a re-oxidizing process may be performed in N₂ gas atmospherein a temperature range of 600 degrees C. to 1000 degrees C.

(Plating Process)

After that, with a plating process, a metal such as Cu, Ni, and Sn maybe coated on the external electrodes 20 a and 20 b.

In the embodiment, the concentration of the rare earth element in theactive region 14 is equal to or more than the concentration of the rareearth element in the protective region. It is therefore possible toreduce the difference of densifying between the active region 14 and theprotective region. In this case, even if the firing temperature is notexcessively increased, it is possible to densify both the active region14 and the protective region. It is therefore possible to suppress thereduction of the continuity modulus of the internal electrode layer 12and improve the humidity resistance. The element promoting thedensifying of the protective region may not be necessarily added. Inthis case, the diffusion of the additive element into the active region14 is suppressed. It is therefore possible to suppress the degradationof the characteristic of the multilayer ceramic capacitor 100. Theaverage ionic radius of the rare earth element in the active region 14is equal to or more than the average ionic radius of the rare earthelement in the protective region. In this case, the grain growth in theprotective region is suppressed. Therefore, the grain growth of theactive region 14 around the protective region is suppressed.Accordingly, it is possible to improve the reliability of the activeregion 14.

In the manufacturing method of the embodiment, the concentration of therare earth element in the active region 14 is equal to or more than theconcentration of the rare earth element in the protective region, andthe average ionic radius of the rare earth element in the active region14 is equal to or more than the average ionic radius of the rare earthelement in the protective region. However, the relationships are notlimited. At least one of the whole of the cover layer 13 and the wholeof the side margin region 16 has only to satisfy the above-mentionedrelationships.

Examples

The multilayer ceramic capacitors in accordance with the embodiment weremade. And, property of the multilayer ceramic capacitors was measured.

(Making of the Dielectric Material)

Additive elements were added to barium titanate powder. The resultingbarium titanate powder and the additive elements were sufficientlywet-blended with each other and crushed in a ball mill. Thus, thedielectric material was obtained. In examples 1, 2 and 4 and acomparative example 1, Dy₂O₃ was weighed so that a concentration of Dywith respect to 100 atm % of barium titanate powder was 1.0 atm %. In anexample 3, Ho₂O₃ was weighed so that a concentration of Ho with respectto 100 atm % of barium titanate was 1.0 atm %. In a comparative example2, Ho₂O₃ was weighed so that a concentration of Ho with respect to 100atm % of barium titanate powder was 0.75 atm %. In a comparative example3, Dy₂O₃ was weighed so that a concentration of Dy with respect to 100atm % of barium titanate powder was 0.75 atm %. In the examples 1 to 4and the comparative examples 1 to 3, MgO, Mn₂O₃ and SiO₂ were weighed sothat a concentration of Mg, a concentration Mn and a concentration of Siwith respect to 100 atm % of barium titanate powder were respectively0.50 atm %, 0.10 atm % and 1.00 atm %.

(Making of the Cover Material and the Side Margin Material)

Additive elements were doped to barium titanate powder. The resultingbarium titanate powder and the additive elements were sufficientlywet-blended with each other and crushed in a ball mill. Thus, the covermaterial and the side margin material were obtained. In the example 1,Ho₂O₃ was weighed so that a concentration of Ho with respect to 100 atm% of barium titanate powder was 0.75 atm %. In the example 2, Ho₂O₃ wasweighed so that a concentration of Ho with respect to 100 atm % ofbarium titanate was 1.0 atm %. In the example 3, Er₂O₃ was weighed sothat a concentration of Er with respect to 100 atm % of barium titanatepowder was 1.0 atm %. In the example 4, Dy₂O₃ was weighed so that aconcentration of Dy with respect to 100 atm % of barium titanate powderwas 0.75 atm %. In the comparative example 1, Ho₂O₃ and Gd₂O₃ wereweighed so that a concentration of Ho and a concentration of Gd withrespect to 100 atm % of barium titanate powder were 0.5 atm % and 0.5atm %. In the comparative example 2, Dy₂O₃ was weighed so that aconcentration of Dy with respect to 100 atm % of barium titanate powderwas 1.0 atm %. In the comparative example 3, Ho₂O₃ was weighed so that aconcentration of Ho with respect to 100 atm % of barium titanate powderwas 1.0 atm %. In the examples 1 to 4 and the comparative examples 1 to3, MgO, Mn₂O₃ and SiO₂ were weighed so that a concentration of Mg, aconcentration Mn and a concentration of Si with respect to 100 atm % ofbarium titanate powder were respectively 0.50 atm %, 0.10 atm % and 1.00atm %.

(Making of the Multilayer Ceramic Capacitor)

Butyral acting as an organic binder, and toluene and ethyl alcoholacting as a solvent were added to the dielectric material. A dielectricgreen sheet was formed by a doctor blade method so that the thickness ofthe dielectric layers 11 after sintering became 1.0 μm. Conductive pastefor forming an internal electrode was screen-printed on the resultingdielectric green sheet, and the internal electrode layer pattern wasformed. 250 numbers of the dielectric green sheets on which theconductive paste for forming an internal electrode were stacked. Coversheets were stacked on a lower face and an upper face of the stackedsheets. The thickness of the cover sheets was 30 Butyral acting as anorganic binder, and toluene and ethyl alcohol acting as a solvent wereadded to the cover material. The cover sheets were formed by a doctorblade method. After that, the resulting multilayer structure was cutinto a predetermined shape. Thereby, the two end faces to which aplurality of internal electrode layer patterns are alternately exposedand the two side faces to which all of the internal electrode layerpatterns are exposed were formed. The side margin sheets are affixed tothe two side faces. The binder was removed from the resulting stackedstructure in N₂ atmosphere. Butyral acting as an organic binder, andtoluene and ethyl alcohol acting as a solvent were added to the sidemargin material. The side margin sheets were formed by a doctor blademethod. After that, Ni external electrodes were formed on the stackedstructure by a dipping method. The resulting stacked structure was firedat a temperature of 1250 degrees C. in a reductive atmosphere (O₂partial pressure: 10⁻⁵ to 10⁻⁸ atm). And sintered structure was formed.The sintered structure had a length of 0.6 mm, a width of 0.3 mm and aheight of 0.3 mm. After re-oxidation of the sintered structure in N₂atmosphere at a temperature of 800 degrees C., Cu, Ni and Sn were coatedon the external electrodes by a plating. Thus, the multilayer ceramiccapacitor was obtained. After the firing, the thickness of the internalelectrode layer of Ni was 1.0 μm.

(Analysis)

The concentrations of the rare earth element of the active region 14 andthe protective region were measured. LA-ICP-MS (Laser AbrationInductively Coupled Plasma-Mass Spectrometry) method was used. Table 2shows the measured concentrations of the rare earth element. The averageionic radiuses were calculated from the measured concentrations and theionic radiuses of Table 1. When the concentration of the rare earthelement in the active region 14 is equal to or more than theconcentration of the rare earth element in the protective region, thecondition of the concentrations of the rare earth element in Table 2 wasdetermined as good “◯”. When the concentration of the rare earth elementin the active region 14 is less than the concentration of the rare earthelement in the protective region, the condition of the concentrations ofthe rare earth element in Table 2 was determined as bad “x”. When theaverage ionic radius of the rare earth element in the active region 14was equal to or more than the average ionic radius of the rare earthelement in the protective region, the condition of the average ionicradius of the rare earth element in Table 2 was determined as good “◯”.When the average ionic radius of the rare earth element in the activeregion 14 was less than the average ionic radius of the rare earthelement in the protective region, the condition of the average ionicradius of the rare earth element in Table 2 was determined as bad “x”.As shown in Table 2, in the examples 1 to 4, the condition of theconcentration of the rare earth element and the condition of the averageionic radius of the rare earth element were determined as good “◯”. Inthe comparative example 1, the condition of the concentration of therare earth element was determined as good “◯”, but the condition of theaverage ionic radius of the rare earth element was determined as bad“x”. In the comparative example 2, both of the condition of theconcentration of the rare earth element and the condition of the averageionic radius of the rare earth element were determined as bad “x”. Inthe comparative example 3, the condition of the average ionic radius ofthe rare earth element was determined as good “◯”, but the condition ofthe concentration of the rare earth element was determined as bad “X”

TABLE 2 RARE EARTH RARE EARTH AVERAGE IONIC DENSITY OF ELEMENT INELEMENT IN CONCENTRATION RADIUS CONDITION PROTECTIVE ACTIVE REGIONPROTECTIVE REGION CONDITION OF OF RARE EARTH REGION (atm %) (atm %) RAREEARTH ELEMENT ELEMENT (g/cc) EXAMPLE 1 Dy 1.0  Ho 0.75 ∘ ∘ 5.8 EXAMPLE 2Dy 1.0 Ho 1.0 ∘ ∘ 5.9 EXAMPLE 3 Ho 1.0  Er 1.0 ∘ ∘ 5.9 EXAMPLE 4 Dy 1.0 Dy 0.75 ∘ ∘ 5.8 COMPARATIVE Dy 1.0 Ho 0.5 ∘ x 5.7 EXAMPLE 1 Gd 0.5COMPARATIVE  Ho 0.75 Dy 1.0 x x 5.0 EXAMPLE 2 COMPARATIVE  Dy 0.75 Ho1.0 x ∘ 5.1 EXAMPLE 3

Next, the density of the protective region (g/cc) was measured. Table 2and Table 3 show the measured results. The higher the density of theprotective region is, the higher the humidity resistance is. When thedensity was more than 5.5 g/cc, the humidity resistance was determinedas good “◯”. When the density was equal to or less than 5.5 g/cc, thehumidity resistance was determined as bad “x”. In the examples 1 to 4and the comparative example 1, the humidity resistance was determined asgood “◯”. It is thought that this was because the condition of theconcentration of the rare earth element was determined as good “◯” inthe examples 1 to 4 and the comparative example 1. On the other hand, inthe comparative examples 2 and 3, the humidity resistance was determinedas bad “X”. It is thought that this was because the condition of theconcentration of the rare earth element was determined as bad “x” in thecomparative examples 2 and 3. The density of the protective region wascalculated from an area ratio of a cavity, which was obtained byobserving a cross section of the grinded multilayer ceramic capacitor bySEM (Scanning Electron Microscope).

TABLE 3 GRAIN DIAMETER OF ACTIVE REGION/ HUMIDITY GRAIN DIAMETER NEARRESISTANCE PROTECTIVE REGION LIFE VALUE DETERMINATION EXAMPLE 1 ∘203/227 nm ∘(220 min) ∘ EXAMPLE 2 ∘ 205/210 nm ∘(328 min) ∘ EXAMPLE 3 ∘192/190 nm ∘(234 min) ∘ EXAMPLE 4 ∘ 207/204 nm ∘(166 min) ∘ COMPARATIVE∘ 201/290 nm x(90 min) x EXAMPLE 1 GRAIN GROWTH NEAR PROTECTIVE REGIONCOMPARATIVE x 211/283 nm x(72 min) x EXAMPLE 2 GRAIN GROWTH NEARPROTECTIVE REGION COMPARATIVE x 220/195 nm ∘(188 min) x EXAMPLE 3

Next, life characteristic was measured. Regarding the lifecharacteristic, life characteristic test was performed with respect to20 samples of each of the examples 1 to 4 and the comparative examples 1to 3. And, an average life value was measured. In the lifecharacteristic test, a direct current voltage of 10 V was applied at 125degrees C. A leak current was measured by a current meter. And a timeuntil breakdown occurs was determined as a life value. When the averagelife value was more than 100 min, the life characteristic was determinedas good “◯”. When the average life value was 100 min or less, the lifecharacteristic was determined as bad “X”. Table 3 shows the measuredresults. In the examples 1 to 4 and the comparative examples 3, the lifecharacteristic was determined as good “◯”. It is thought that this wasbecause the condition of the average ionic radius of the rare earthelement was good “◯”. On the other hand, in the comparative examples 1and 2, the life characteristic was determined as bad “x”. It is thoughtthat this was because the average ionic radius of the rare earth elementof the protective region was larger than the average ionic radius of therare earth element of the active region 14, grain growth was promoted inthe protective region, and grain growth was promoted in the part of theactive region 14 near the protective region because of the influence ofthe protective region.

And so, as illustrated in FIG. 5, a grain diameter of a ceramic crystalof a center region α of the active region 14 and a grain diameter of aceramic crystal of a region β near the protective region were measured.Table 3 shows measured results. As shown in Table 3, there was not alarge difference between the ceramic crystal grain diameter of thecenter region α of the active region 14 (grain diameters of the activeregion in Table 3) and the ceramic crystal grain diameter of the regionβ near the protective region (grain diameters of the protective regionin Table 3), in the examples 1 to 4 and the comparative example 3. Inthis manner, in the examples 1 to 4 and the comparative example 3, itwas confirmed that the grain growth was suppressed in the active region14. On the other hand, in the comparative examples 1 and 2, the ceramiccrystal grain diameter of the region β near the protective region wasgreatly larger than that of the center region α in the active region 14.In this manner, it was confirmed that the grain growth was promoted inthe region β of the active region 14, in the comparative examples 1 and2.

Although the embodiments of the present invention have been described indetail, it is to be understood that the various change, substitutions,and alterations could be made hereto without departing from the spiritand scope of the invention.

What is claimed is:
 1. A multilayer ceramic capacitor comprising: amultilayer structure in which each of a plurality of dielectric layersand each of a plurality of internal electrode layers are alternatelystacked, a main component of the dielectric layers being ceramic, themultilayer structure having a rectangular parallelepiped shape, theplurality of internal electrode layers being alternately exposed to afirst end face and a second end face of the multilayer structure, thefirst end face facing the second end face, wherein a concentration of arare earth element in an active region with respect to a main componentceramic of the active region is equal to or more than a concentration ofa rare earth element in at least a part of a protective region withrespect to a main component ceramic of the protective region, whereinthe active region is a region in which a set of internal electrodelayers exposed to the first end face of the multilayer structure faceanother set of internal electrode layers exposed to the second end faceof the multilayer structure, wherein the protective region includes acover layer and a side margin, wherein the cover layer is provided on atleast one of an upper face and a lower face of the multilayer structurein a stacking direction of the multilayer structure, a main component ofthe cover layer being a same as that of the dielectric layers, wherein,in the multilayer structure, the side margin covers edge portions towhich the plurality of internal electrode layers extend toward two sidefaces other than the first end face and the second end face, wherein anaverage ionic radius of the rare earth element of the at least a part ofthe protective region is less than an average ionic radius of the rareearth element in the active region, wherein the concentration of rareearth elements in the protective region with respect to the maincomponent ceramic is 0.5 atm % or more and 2.0 atm % or less, andwherein a density of the protective region is more than 5.5 g/cc.
 2. Themultilayer ceramic capacitor as claimed in claim 1, wherein an averagethickness of the dielectric layers is 1 μm or less.
 3. The multilayerceramic capacitor as claimed in claim 1, wherein the at least a part ofthe protective region is one of a whole of the cover layer and a wholeof the side margin.
 4. The multilayer ceramic capacitor as claimed inclaim 1, wherein the main component ceramic of the dielectric layers andthe protective region is barium titanate.
 5. The multilayer ceramiccapacitor as claimed in claim 1, wherein the rare earth element added tothe active region is at least one of Gd, Tb, Dy, Ho, Er, Y and Yb, andwherein the rare earth element added to the protective region is atleast one of Gd, Tb, Dy, Ho, Er, Y and Yb.
 6. A manufacturing method ofthe multilayer ceramic capacitor of claim 1, comprising: a first processof forming a stack unit by providing a pattern of metal conductive pasteon a green sheet having grains of main component ceramic whichcorresponds to the main component ceramic of the active region; a secondprocess of stacking a plurality of the stack units formed in the firstprocess in a manner that positions of the patterns are alternatelyshifted to each other so that the plurality of internal electrode layersare alternately exposed to the first end face and the second end face ofthe multilayer structure of the multilayer ceramic capacitor; and athird process of providing a cover sheet on at least one of an upperface and a lower face in a stacking direction of a ceramic multilayerstructure obtained in the second process which corresponds to themultilayer structure of the multilayer ceramic capacitor, the coversheet corresponding to the cover layer and including grains of maincomponent ceramic which is the same as the main component ceramic of theactive region, said third process further comprising providing the sidemargin of the multilayer structure of the multilayer ceramic capacitor,forming the protective region together with the cover layer, wherein aconcentration of a rare earth element in the green sheet with respect tothe main component ceramic of the green sheet is equal to or more than aconcentration of a rare earth element in the cover sheets with respectto the main component ceramic of the cover so that the concentration ofthe rare earth element in the active region with respect to the maincomponent ceramic of the active region is equal to or more than theconcentration of the rare earth element in at least the part of theprotective region with respect to the main component ceramic of theprotective region, said concentration of the rare earth elements in theprotective region with respect to the main component ceramic being 0.5atm % or more and 2.0 atm % or less, wherein an average ionic radius ofthe rare earth element of the cover sheets and/or an average ionicradius of the rare earth element of the side margin sheet are/is lessthan an average ionic radius of the rare earth element of the greensheet so that the average ionic radius of the rare earth element of theat least a part of the protective region is less than the average ionicradius of the rare earth element in the active region, and wherein adensity of the protective region is more than 5.5 g/cc.
 7. A multilayerceramic capacitor comprising: a multilayer structure in which each of aplurality of dielectric layers and each of a plurality of internalelectrode layers are alternately stacked, a main component of thedielectric layers being ceramic, the multilayer structure having arectangular parallelepiped shape, the plurality of internal electrodelayers being alternately exposed to a first end face and a second endface of the multilayer structure, the first end face facing the secondend face, wherein a concentration of a rare earth element in an activeregion with respect to a main component ceramic of the active region isequal to or more than a concentration of a rare earth element in a sidemargin with respect to a main component ceramic of the side margin,wherein the active region is a region in which a set of internalelectrode layers exposed to the first end face of the multilayerstructure face another set of internal electrode layers exposed to thesecond end face of the multilayer structure, wherein, in the multilayerstructure, the side margin covers edge portions to which the pluralityof internal electrode layers extend toward two side faces other than thefirst end face and the second end face, and wherein an average ionicradius of the rare earth element of the side margin is less than anaverage ionic radius of the rare earth element in the active region. 8.The multilayer ceramic capacitor as claimed in claim 1, wherein the rareearth element in the protective region is holmium (Ho) where the rareearth element in the active region is dysprosium (Dy), and the rareearth element in the protective region is erbium (Er) where the rareearth element in the active region is holmium (Ho).
 9. The multilayerceramic capacitor as claimed in claim 7, wherein the rare earth elementin the side margin is holmium (Ho) where the rare earth element in theactive region is dysprosium (Dy), and the rare earth element in the sidemargin is erbium (Er) where the rare earth element in the active regionis holmium (Ho).